1,256 research outputs found
Post-Newtonian Gravitational Radiation
1 Introduction 2 Multipole Decomposition 3 Source Multipole Moments 4
Post-Minkowskian Approximation 5 Radiative Multipole Moments 6 Post-Newtonian
Approximation 7 Point-Particles 8 ConclusionComment: 46 pages, in Einstein's Field Equations and Their Physical
Implications, B. Schmidt (Ed.), Lecture Notes in Physics, Springe
Quantized Fourier and Polynomial Features for more Expressive Tensor Network Models
In the context of kernel machines, polynomial and Fourier features are
commonly used to provide a nonlinear extension to linear models by mapping the
data to a higher-dimensional space. Unless one considers the dual formulation
of the learning problem, which renders exact large-scale learning unfeasible,
the exponential increase of model parameters in the dimensionality of the data
caused by their tensor-product structure prohibits to tackle high-dimensional
problems. One of the possible approaches to circumvent this exponential scaling
is to exploit the tensor structure present in the features by constraining the
model weights to be an underparametrized tensor network. In this paper we
quantize, i.e. further tensorize, polynomial and Fourier features. Based on
this feature quantization we propose to quantize the associated model weights,
yielding quantized models. We show that, for the same number of model
parameters, the resulting quantized models have a higher bound on the
VC-dimension as opposed to their non-quantized counterparts, at no additional
computational cost while learning from identical features. We verify
experimentally how this additional tensorization regularizes the learning
problem by prioritizing the most salient features in the data and how it
provides models with increased generalization capabilities. We finally
benchmark our approach on large regression task, achieving state-of-the-art
results on a laptop computer
Best network chirplet-chain: Near-optimal coherent detection of unmodeled gravitation wave chirps with a network of detectors
The searches of impulsive gravitational waves (GW) in the data of the
ground-based interferometers focus essentially on two types of waveforms: short
unmodeled bursts and chirps from inspiralling compact binaries. There is room
for other types of searches based on different models. Our objective is to fill
this gap. More specifically, we are interested in GW chirps with an arbitrary
phase/frequency vs. time evolution. These unmodeled GW chirps may be considered
as the generic signature of orbiting/spinning sources. We expect quasi-periodic
nature of the waveform to be preserved independent of the physics which governs
the source motion. Several methods have been introduced to address the
detection of unmodeled chirps using the data of a single detector. Those
include the best chirplet chain (BCC) algorithm introduced by the authors. In
the next years, several detectors will be in operation. The joint coherent
analysis of GW by multiple detectors can improve the sight horizon, the
estimation of the source location and the wave polarization angles. Here, we
extend the BCC search to the multiple detector case. The method amounts to
searching for salient paths in the combined time-frequency representation of
two synthetic streams. The latter are time-series which combine the data from
each detector linearly in such a way that all the GW signatures received are
added constructively. We give a proof of principle for the full sky blind
search in a simplified situation which shows that the joint estimation of the
source sky location and chirp frequency is possible.Comment: 22 pages, revtex4, 6 figure
Self-force with (3+1) codes: a primer for numerical relativists
Prescriptions for numerical self-force calculations have traditionally been
designed for frequency-domain or (1+1) time-domain codes which employ a mode
decomposition to facilitate in carrying out a delicate regularization scheme.
This has prevented self-force analyses from benefiting from the powerful suite
of tools developed and used by numerical relativists for simulations of the
evolution of comparable-mass black hole binaries. In this work, we revisit a
previously-introduced (3+1) method for self-force calculations, and demonstrate
its viability by applying it to the test case of a scalar charge moving in a
circular orbit around a Schwarzschild black hole. Two (3+1) codes originally
developed for numerical relativity applications were independently employed,
and in each we were able to compute the two independent components of the
self-force and the energy flux correctly to within . We also demonstrate
consistency between -component of the self-force and the scalar energy flux.
Our results constitute the first successful calculation of a self-force in a
(3+1) framework, and thus open opportunities for the numerical relativity
community in self-force analyses and the perturbative modeling of
extreme-mass-ratio inspirals.Comment: 23 pages, 13 figure
Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)
The implicit objective of the biennial "international - Traveling Workshop on
Interactions between Sparse models and Technology" (iTWIST) is to foster
collaboration between international scientific teams by disseminating ideas
through both specific oral/poster presentations and free discussions. For its
second edition, the iTWIST workshop took place in the medieval and picturesque
town of Namur in Belgium, from Wednesday August 27th till Friday August 29th,
2014. The workshop was conveniently located in "The Arsenal" building within
walking distance of both hotels and town center. iTWIST'14 has gathered about
70 international participants and has featured 9 invited talks, 10 oral
presentations, and 14 posters on the following themes, all related to the
theory, application and generalization of the "sparsity paradigm":
Sparsity-driven data sensing and processing; Union of low dimensional
subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph
sensing/processing; Blind inverse problems and dictionary learning; Sparsity
and computational neuroscience; Information theory, geometry and randomness;
Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?;
Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website:
http://sites.google.com/site/itwist1
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